custom derailer hanger on track ends

Ok so this may sound a bit odd but I have at the moment a EAI brassknuckle frame that I would like to convert into a track/TT crossover frame. I havent ever ventured into the world of gears since i was a young child and Im not sure if this is even possible. Can I have a derailer hanger tig welded to my frame (aluminum). and then run a single chainring out front with a 7speed cassette on the rear. After riding fixed for a few years All I really want is a few gears for making it up hills or for a little more speed on flats. would it be cheaper to buy a new frame or should i just get this idea out of my head all together?